Ok, so he is in theory "between life and death," but they don't quite know what's wrong with him, so they do some nice simple diagnostic tests like a colonoscopy and a BIOPSY OF THE SPINAL CORD??
One of the "teaching tools" we had in medical school was a computer program that gave you a case in the ER and had you select various things to do. They have such things now as well, but better. Anyway, one of the choices selectable was a brain biopsy. Why, exactly, I have no idea, since if you have to do a brain biopsy in the ER you are really screwed.